486 



•TIMBER RESOURCES FOR AMERICA'S FUTURE 



Table 290. — Rates of mortality and gross growth of sawtimber jor the initial year oj projection periods, 



by levels of demand and species groups 



Demand level and species group 



Gross growth rate ' 



1985 rate 



in relation 



to 1953 



rate 



Mortality rate 



1985 rate 

 in relation 



1953 



1975 



1985 



1953 



1975 



1985 



to 1953 

 rate 



Lower level: 



Eastern hardwoods 



Percent 

 5.76 

 8.05 

 1. 44 



Percent 

 5.01 

 7.39 

 1. 95 



Percent 

 4.55 

 6. 80 

 2. 21 



Percent 

 -21 

 -16 

 + 53 



Percent 



0.60 



.66 



.63 



Percent 



0.47 



.48 



. 55 



Percent 



0. 45 



. 45 



.52 



Percent 

 — 25 



Eastern softwoods 



-32 



Western species 



— 17 







All species 



3.00 



3. 58 



3. 70 



+ 23 



.63 



.52 



.49 



-22 







Medium level: 



Eastern hardwoods 



5. 76 

 8.05 

 1. 44 



5. 13 



7. 64 

 1.97 



4. 69 

 7.35 

 2.26 



-19 

 -9 



+ 57 



. 60 

 . 66 

 .63 



. 47 

 .49 

 .54 



.45 

 . 47 

 .52 



— 25 



Eastern softwoods 



— 29 



Western species. 



— 17 







All species . _ . 



3. 00 



3.63 



3.74 



+ 25 



.63 



. 51 



.49 



— 22 







1 Includes ingrowth. 



Eastern forests consist largely of yoimg trees 

 growing at rapid rates. As the inventory builds 

 up in accordance with expected forestry trends 

 and as these forests become older, the volume of 

 growth will increase but rates of growth will de- 

 cline. This decline is in accord with well-estab- 

 lished knowledge of the relationships between the 

 growth rates and the ages of forest stands. Thus, 

 growth rates for eastern hardwoods and eastern 

 softwoods in 1975 and 1985 are lower than the 

 1953 rates. 



Mortality rates, derived by procedures similar 

 to those used for rates of gross growth, reflect 

 expectations of steadily declining losses from fire, 

 insects, disease, and other natural causes. For 

 all species combined, the mortality rate of 0.63 

 percent in 1953 drops to 0.49 percent in 1985, a 

 decrease of 22 percent. 



These changes in rates of gross growth and 

 mortality are an overall expression of the allow- 

 ances made in projections for the increased in- 

 tensity of forestr}^ expected from continuation of 

 recent trends. 



Projected Growth Compared to 1952 

 Growth 



Growth Declines Under Medium Level 

 Demands After 1975 



With medium level demands met each year and 

 with forestry progressing as indicated b}- recent 

 trends, projected growth of sawtimber will rise 

 from 47.4 billion board-feet in 1952 to 58.6 billion 

 board-feet in 1975 — an increase of 24 percent 

 (table 291). In 1975 projected growth of both 

 eastern hardwoods and eastern softwoods is 18 



percent more than in 1952, while western species 

 increase 41 percent. 



Timber removal at the medium level would in- 

 crease from 68.2 billion board-feet in 1975 to 

 105.4 billion board-feet in 2000. During this 

 period the large and rapidly increasing timber 

 removal would exceed growth by successively 

 larger amounts, and the accompanying reduction 

 of inventory would result in a sharp decline in 

 growth late in the century. When growth pro- 

 jection calculations are followed through after 

 1975 under the basic assumptions, a decrease of 

 47 percent in sawtimber growth of all species bv 

 2000 is indicated (table 291). Growth of eastern 

 hardwoods would be 36 percent less in 2000 than 

 in 1952, growth of eastern softwoods would be 

 negligible, and growth of western species would 

 increase 15 percent. 



These statistics are useful chiefly to show that 

 the progress in forestry indicated by recent trends 

 will fall far short of supplying medium level de- 

 mands. In all probabilitjr, economic factors not 

 included in the basic assumptions will become 

 operative at some time prior to 2000 and not only 

 reduce timber removal below the level needed to 

 supply projected demands but also raise growth 

 above the calculated volimies. These factors are 

 discussed under the heading Needed Growth 

 Compared to Projected Growth. 



In terms of growing stock, projections indicate 

 that growth in 1975 would be 19 percent more 

 and in 2000, 14 percent less than growth in 1952. 

 Growth of eastern softwoods would rise slightlv 

 between 1952 and 1975 but by 2000 would be 86 

 percent less than 1952 growtli. By 2000, pro- 

 jected growth of eastern hardwoods and western 

 species is 13 percent and 32 percent, respectively, 

 above 1952 growth. Although these projected 

 trends appear more favorable than those for 



